Optical pattern generator using a single rotating component

ABSTRACT

An optical pattern uses a single rotating component. The rotating component includes a number of deflection sectors. Each sector deflects an incident optical beam by a substantially constant angular amount although this amount may vary from one sector to the next. The rotating component may be combined with an imaging lens group that produces, for example, image points, spots, or lines displaced along a line locus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/620,200,filed Nov. 17, 2009, which is a divisional of application Ser. No.12/119,461, filed May 12, 2008, now U.S. Pat. No. 7,646,522, which is adivisional of application Ser. No. 11/158,907, filed Jun. 20, 2005, nowU.S. Pat. No. 7,372,606, which claims the benefit of U.S. ProvisionalApplication No. 60/652,891, filed Feb. 14, 2005, and application Ser.No. 11/158,907 is a continuation-in-part of application Ser. No.10/750,790, filed Dec. 31, 2003, now U.S. Pat. No. 7,184,184. Thedisclosure of each of these documents is hereby incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

This invention relates generally to optically generating a pattern offigures such as arrays of image points, spots, or lines. Moreparticularly, this invention relates to generating such patterns using asingle rotating component that has a plurality of deflection sectorsthat deflect an incident optical beam by various amounts.

The optical generation of a pre-defined pattern of spots or scan linesis used in a variety of applications. Digital copiers, printers,fingerprint identification, hand-held bar code scanners, industrialapplications, light show entertainment, displays, telecommunicationsswitching and medical applications are a few examples. Perhaps the mostcommon mechanisms for generating patterns of figures are tilting minors(e.g., oscillating minors driven by galvanometers) and reflections fromrotating convex polygons.

However, optical pattern generators based on tilting minors typicallyhave characteristics that make them unsuitable for certain applications.For example, scanning in these systems is typically achieved by tiltinga mirror back and forth. But back and forth motion requires that theminor come to a stop and then reverse direction. This takes time, whichlimits the scan rate. In order to increase the scan rate of thesesystems, the mirror often is driven with an oscillating motion at a ratethat is near its resonant frequency. However, this severely restrictsthe patterns that can be generated. For example, it is difficult togenerate irregular patterns since the mirror motion is constrained to beoscillatory. The near-resonance condition also limits the range of scanrates that can be achieved. For example, it is difficult to tune such asystem over a wide range of scan rates since the near-resonancecondition cannot be met over a wide range. In addition, the angular scanvelocity of resonant scanners is usually sinusoidal and not suitable fora large number of applications where dwell time at each point must bereasonable constant.

If a two-dimensional pattern is desired (e.g., a series of parallel scanlines or a two-dimensional pattern of spots), then typically either asingle mirror is tilted in two directions simultaneously or twocoordinated, tilting mirrors are used. In many cases the efficiency ofthe utilization of light, such as laser light, is also important. Theefficiency may be defined as the fraction of energy deposited in adesired pattern on the treatment surface compared to the total energyproduced by the light source in a given period of time. If a pattern issparse compared to the background, it is preferable to turn off thelight source and scan quickly over the background, and then turn it backon when the light beam has settled over the spot to be exposed andexpose the spots in the pattern in such a manner that the light sourceis efficiently utilized in time. This requires an even more responsivedevice that can accelerate, decelerate and settle quickly. As a resultof these characteristics, galvanometer-based systems and convex polygonsystems are not well suited for high speed pattern generation,particularly if the pattern is an irregular or a sparse one.

In the rotating polygon approach, the sides of a three-dimensionalpolygon are mirrored and the polygon is rotated about a center axis. Aseach mirrored side rotates through an incident optical beam, the opticalbeam is reflected to generate a point on a scan line. The rotation ofeach mirrored side through the optical beam produces one scan line. Ifall of the mirrored sides are the same (e.g., make the same pyramidangle with the base of the polygon), then the same scan line is tracedover and over. If the mirrored sides are different, then different scanlines can be traced as each side rotates through the optical beam. Forexample, by varying the pyramid angle of each side, the reflectedoptical beam can trace a series of scan lines.

However, the rotating polygon approach also has drawbacks that make itunsuitable for certain applications. For example, systems that produce aseries of scan lines can suffer from aberrations due to the rotation. Inorder to trace a series of scan lines, each side has a different pyramidangle that offsets the basic scan line in a direction that isperpendicular to the scan direction. However, as each side rotatesthrough the optical beam, the orientation of the angled side is alsorotated. This can cause changes in the amount of offset and/or otherunwanted aberrations. One example is scan line bow. The ideal scan lineis generally a straight line segment but the actual scan line is oftenan arc segment. The sag of the arc segment is the bow. In the case ofrotating polygon scanners, sides that have non-zero pyramid anglesgenerate bowed scan lines. The amount of bowing depends on the pyramidangle. In a polygon scanner where different pyramid angles are used totrace multiple scan lines or to generate spots at different locations,not only will each scan line be bowed, but the bow will vary from onescan line to the next. The difference between the bow of the top-mostscan line and the bottom-most scan line can be significant.

Scan line bow and other effects caused by rotation can cause additionalproblems, depending on the application. For example, in someapplications, the scanning action is used to compensate for motion ofthe scanner relative to a target so that the optical beam ideallyremains at a fixed spot on the target even though the scanner is movingrelative to the target. In this case, scan line bow will cause theoptical beam to move in the direction perpendicular to the scandirection. If this motion is slow compared to the dwell time of theoptical beam on the target, then the bow effectively introduces anunwanted motion in the perpendicular direction. If the motion is fastrelative to the dwell time of the optical beam on the target, then thebow, which is a radial deflection, when combined with the uncompensatedtangential motion, effectively blurs the optical beam, increasing thespot size of the beam on the target. Typically, neither effect isdesirable.

Thus, there is a need for optical pattern generators than can operate athigh speeds with long dwell times at each image point, particularly forthe generation of irregular patterns. There is also a need for patterngenerators with reduced aberrations and/or image blurring.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art byproviding an optical pattern generator using a single rotatingcomponent. The rotating component includes a number of deflectionsectors containing optical elements. Each sector deflects an incidentoptical beam by a substantially constant angle although this angle mayvary from one sector to the next. The rotating component may be combinedwith an imaging group that produces, for example, image points, spots,or lines displaced along a line locus. The image spots can also bedisplaced to either side of a line, for example by introducing a tilt inthe orthogonal direction.

This approach can result in many advantages. The use of a singlerotating component with sectors that are positioned contiguously aroundits periphery can provide a high radiometric efficiency. The geometry ofa rotating component such as a thin disk with optical elements locatedon the periphery facilitates rotation at high angular velocities, thusproducing image patterns at high rates of speed. The angular velocity ofthe rotating component combined with the pseudo-stationary angulardeflection can be used to cause the individual image points, spots, orlines to deliver high radiant energy doses to a small point in the imagespace with high radiometric efficiency. The angular deflection ispseudo-stationary in the sense that each deflection sector produces anapproximately constant angular deflection as it rotates through theincident optical beam, but each deflection sector can have a differentconstant angular deflection.

Another advantage of a single rotating component compared to twocounter-rotating components is that the synchronization between twocounter-rotating components and its attendant high cost is avoided. Thedrive mechanism for a single rotating component is less complex than fortwo counter-rotating components because the angular velocity can berapidly changed without the additional requirement of maintainingsynchronism. The use of one rather than two rotating components can alsoreduce size and weight. The packing geometry of the optical elements canalso result in a more compact rotating component, and the number ofcomponents with their attendant cost can be significantly reduced.

In one aspect of the invention, the preferred embodiments use reflectivesurfaces which permit the optical pattern generator to be independent ofthe wavelengths of the incident optical beams and thereby permits thesimultaneous identical pattern generation of several differentwavelengths in applications that can benefit from this condition.

In one application, a scanner produces optical patterns that consist ofspots or line segments displaced along a straight line locus. Twodimensional patterns are developed by movement of the target area withrespect to the pattern generator. Implementations of the presentinvention can utilize this “painting” concept but can also providepatterns that have a “zig-zag” image point pattern. The use of zig-zagimage point patterns in certain applications has the advantage ofpreventing thermal interaction between neighboring image points, forexample sparing biologic tissue from damage and preventing accidentalcutting of biologic tissue.

In certain embodiments, an optical pattern generator includes a singlerotating component that has a plurality of deflection sectors arrangedon the outer periphery of a rotating disk. The incident optical beampropagates in the plane of rotation for the disk. The disk presents itsedge, which contains the sectors, to the incident optical beam. Thesectors travel through the incident optical beam as the disk rotates.Each sector includes a pair of opposing planar mirrors which havesurface normals that are also in the plane of rotation. The incidentoptical beam reflects from one mirror to the other minor andsubsequently exits the rotating component at a deflection angle that isroughly ninety degrees relative to the optical beam's incidence angle.The optical path through the mirrors lies primarily in the plane of thedisk. This arrangement of two mirrors has the quality that thedeflection angle does not change as the pair of minors rotates throughthe incident optical beam. Therefore, the pair of minors at theperiphery of a rotating disk component will move through the incidentoptical beam and produce an exit optical beam that has a constantdeflection angle with respect to the incident optical beam. Successivepairs of mirrors (i.e., different sectors) may have different includedangles such that different pairs of minors can deflect the exit opticalbeam by different amounts. This geometry therefore produces apseudo-stationary deflection (PSD) pattern generation.

This example geometry produces an output optical beam from the rotatingcomponent that is collimated (assuming a collimated incident opticalbeam). The output optical beam can be presented to subsequent imagingoptics at a set of selectable beam angles corresponding to differentsectors. The subsequent imaging optics can include a simple reflectiveobjective that produces an image pattern that is independent of thewavelengths present in the incident beam. Refractive, diffractive, orholographic objective systems can also be used.

For this embodiment, example image patterns include a series of imagepoints displaced along an image line locus if the reflective surfaceshave a tilt component in only a single direction. The image pattern caninclude image points displaced in a zig-zag pattern along the image linelocus if the reflective surfaces also have a small tilt component in theorthogonal direction.

To reduce thermal blooming or other unwanted effects due to thesequential irradiation of adjacent image points, the sectors on therotating component can be designed such that non-neighboring points inthe image pattern are sequentially irradiated without reducing the speedor radiometric efficiency of the system. Galvanometric and other patterngenerators typically do not have this capability.

Another embodiment uses pairs of planar mirrors arranged in a rhomboidconfiguration. One mirror of each pair on one side of the rotatingcomponent corresponds with a second minor on the opposing side of therotating component. The incident optical beam is reflected from thefirst mirror, passes across the center of the rotating disk component,and reflects from the second mirror of the minor pair. The tilt anglesfor the mirror pairs are approximately at 45 degrees with respect to theincident or outgoing optical beams. In one embodiment, the tilt anglefor each mirror of one minor pair is at 45 degrees, and the tilt anglesfor other mirror pairs changes slightly such that the outgoing opticalbeam exits at a different angle relative to the incident beam angle.This geometry also maintains the exit beam angle invariance condition.As long as the incident beam is on a selected mirror pair, the exit beamangle is invariant with respect to rotation of the mirror pair. Theexiting beams are PSD invariant as for the previous embodiment. Anycombination of an even number of mirrors rotating together in a planecontaining an incident optical beam can be designed to have the propertyof PSD pattern generation.

Other embodiments use a single rotating component where the incidentoptical beam originates outside the rotating component and propagates ina direction that is not in the plane of rotation for the rotatingcomponent. For example, the incident optical beam may be directed ontotwo optical surfaces placed on a disk that presents its face to theincident optical beam.

In an embodiment based on this geometry, sectors comprise two minors ina ‘Z-folded’ arrangement that causes the exit optical beam to beapproximately collinear to the incident optical beam. Each sector canhave a different included angle between the minors in the sector, suchthat different sectors cause different angular deflections. The twominors can be planar or they can be sections of larger parent surfacesof revolution such as spheres or aspheres. Angular deflection can bemaintained at a nearly constant level by making the optical axes of eachmirror surface coincident with the rotation axis of the disk so thatrotation of the disk does not change the form of the optical surfacespresented to the incident optical beam.

In yet other embodiments, a single rotating component has sectorsarranged around the periphery, similar to the cylindrical section of abarrel. The incident optical beam is injected from inside thecylindrical section. These embodiments preferably use transmissiveoptical elements instead of reflective optical elements, but reflectivesurfaces can also be used for example when wavelength independence isimportant. Transmissive diffractive structures on the outer surface ofthe cylinder are the preferred optical elements.

The optical pattern generators described above can be used for variousapplications. For example, they can be used to deposit optical energyonto human tissue, either externally onto the skin for example orinternally through various orifices. The optical energy can be used toaccomplish different purposes: local heating, ablation, cutting orcauterizing for example. The devices can also be used to deposit opticalenergy onto other materials: metal, powders, or other industrialmaterials for example. Cutting, welding, ablation and marking areexamples of manufacturing processes that can be implemented. The devicescan also be used in laser or LED printers, optical imaging scanners, orcopy machines. Other applications will be apparent.

Other aspects of the invention include methods corresponding to thedevices, systems and applications described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention has other advantages and features which will be morereadily apparent from the following detailed description of theinvention and the appended claims, when taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a side view of an optical pattern generator according to theinvention, where the incident optical beam lies substantially in theplane of rotation.

FIG. 1B is a close-up showing tilting of the prisms in FIG. 1A.

FIGS. 2A and 2B are a side view and end view, respectively, of theoptical pattern generator of FIG. 1 combined with a reflective imaginggroup.

FIG. 3 is a detail view of the focal area of the system of FIG. 2.

FIG. 4 is a side view illustrating the principle of operation of anotheroptical pattern generator according to the invention, where the incidentoptical beam has a substantial component in a direction normal to theplane of rotation and the full parent surfaces of the reflectivesegments are shown.

FIGS. 5A-5C are a side view, perspective view and top view,respectively, of the optical pattern generator of FIG. 4 combined with areflective imaging group.

FIG. 6 is a side view of another optical pattern generator usinganamorphic aspheric surface segments and a refractive imaging group.

FIG. 7 is a side view of another optical pattern generator usingdiffractive elements on the top of a disk shaped substrate.

FIG. 8 is a side view of another optical pattern generator withdiffractive elements on the side of a barrel shaped substrate.

FIGS. 9A-9B are a side view and perspective view, respectively, of anindustrial welding application using the optical pattern generator ofFIG. 1.

FIGS. 9C and 9D illustrate welding patterns that can be produced fromscanners similar to those shown in FIGS. 9A-9B.

FIG. 10 illustrates another optical pattern generator using a rhomboidminor geometry.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a side view of an optical pattern generator according to theinvention, where the incident optical beam 1 lies substantially in theplane of rotation of rotatable component 9. In this example, therotating component 9 is divided into twenty nine sectors 8A, 8B, 8C,etc., which are arranged in a circle centered on the rotation axis 4 ofthe rotating component 9. The incident optical beam 1 propagates along adirection that lies in the plane of rotation. Each sector 8 includes apair of reflective elements (e.g., reflective surfaces 2 and 3 for thesector that is currently active). The surface normals of the reflectivesurfaces have a substantial component in the plane of rotation. In thisexample, the rotating component 9 includes prisms 6, 7, etc. that arearranged in a circle. The faces of the prisms are reflectively coatedand the reflectively coated surfaces from adjacent prisms (e.g.,reflective surfaces 2 and 3 from prisms 6 and 7) form the opposingreflective surfaces for a sector. Discrete structures other than prismscan also be used and the reflective surfaces need not be planar. Smallflat minors can be used in the place of the prism components.

As the component 9 rotates, the sectors 8 rotate through the incidentoptical beam 1. Each sector 8 deflects the incoming optical beam 1 bysome angular amount. The sectors 8 are designed so that the angulardeflection is approximately constant as each sector rotates through theincident optical beam 1, but the angular deflection may vary from sectorto sector. In more detail, the incident optical beam 1 reflects from thefirst reflective surface 2 on prism 6, and subsequently reflects fromreflective surface 3 on prism 7 before exiting as output optical beam 5.

The two reflective surfaces 2 and 3 form a Penta minor geometry. An evennumber of reflective surfaces that rotate together in the plane of thefolded optical path has the property that the angular deflection isinvariant with the rotation angle of the reflective surfaces. In thiscase, there are two reflective surfaces 2, 3 and rotation of the disk 9causes the prisms 6, 7 and their reflective surfaces 2, 3 to rotatetogether in the plane of the folded optical path. As a result, theoutput beam angle 5 does not change as the two reflective surfaces 2, 3rotate through the incident optical beam 1. The reflective surfaces 2, 3are self-compensating with respect to rotation of the disk 9.Furthermore, if the reflective surfaces 2, 3 are planar, they will alsobe substantially spatially invariant with respect to disk wobble.

As the disk 9 rotates clockwise to the next sector 8 and the next tworeflective surfaces, the angular deflection can be changed by using adifferent included angle between the opposing reflective surfaces. Forthis configuration, the beam will be deflected by an angle that is twicethat of the included angle. For example, if the included angle forsector 8A is 45 degrees, sector 8A will deflect the incident opticalbeam by 90 degrees. If the included angle for sector 8B is 44.5 degrees,then the incident optical beam will be deflected 89 degrees, and so on.In this example, different included angles are used for each of thesectors so that each sector will produce an output optical beam that isdeflected by a different amount. However, the deflection angle will besubstantially invariant within each sector due to the even number ofreflective surfaces rotating together through the incident beam. Forthis example, the angular deflections have a nominal magnitude of 90degrees and a variance of −15 to +15 degrees from the nominal magnitude.

In this example, the apex angle of each prism is 32.5862 degrees,calculated as follows. Each sector 8 subtends an equal angular amount.Since there are twenty nine sectors, each sector subtends 360/29=12.4138degrees as shown in FIG. 1B. The two prisms 6 and 7 have the same shapeand, therefore, the same apex angle β. The component 9 is designed sothat when the included angle is 45 degrees, the prisms 6 and 7 arepositioned so that the line that bisects the apex angle also passesthrough the rotation axis 4. Therefore, the design must satisfy theequation β/2+12.4138+β/2=45. Solving yields an apex angle of β=32.5862degrees.

The next prism 17 moving counterclockwise on the disk 9 from prism 6 istilted slightly by an angle +α so its bisecting line 17L does not passthrough the center of rotation 4 of the disk. As a result, the includedangle for the sector formed by prisms 6 and 17 is(β/2+α)+12.4138+β/2=45+α. The next prism 16 is once again aligned withthe rotation center 4, so the included angle for the sector formed byprisms 16 and 17 is (β/2−α)+12.4138+β/2=45−α. The next prism is tiltedby +2α, followed by an aligned prism, and then a prism tilted by +3α,followed by another aligned prism, etc. This geometry is maintainedaround the periphery of disk 4. This specific arrangement producestwenty nine deflection angles that vary over the range of −15 degrees to+15 degrees relative to the nominal 90 degree magnitude. Note that thisapproach uses an odd number of sectors where every other (approximately)prism is aligned and the alternate prisms are tilted by angles α, 2α,3α, etc.

Other numbers of sectors and different deflection angle patterns can beproduced by variants of this specific geometry. In addition, otherrotation schemes are possible that produce the same angular deflectionbut do not produce them in monotonically increasing order. As anotherexample, the rotating component could have an even number of sectors andprisms, with every other prism aligned and the alternate prisms tiltedby angles α/2, 3α/2, 5α/2, etc. This would produce a set of angulardeflections centered around a nominal magnitude, but without producing adeflection actually at the nominal magnitude.

In another approach, the rotation scheme causes the angular deflectionsto be arranged in a sequence such that the final delivered spots are notproduced in sequential order. In other words, if the pattern is an arrayof spots 1, 2, 3, . . . 29, the sectors may be designed to generate thespots in an order other than sequentially from 1 to 29. For certainapplications, producing adjacent spots within a short period of time cancause thermal coupling between the irradiated regions, and this can bedeleterious to proper treatment. By arranging the prisms appropriately,the spots can be delivered such that temporally successive spots arespatially separated from each other while still delivering the fullpattern of spots.

There is another geometric symmetry that is beneficial for someapplications. Certain applications benefit by image patterns that arearranged to be in a zig-zag rather than a straight line geometry. Forexample, in some biologic applications, if the image spots are arrangedalong a straight line and high irradiance levels are present, theirradiation may accidentally cut tissue in the manner of a laserscalpel. Depositing the image spots in a zig-zag pattern substantiallyreduces the propensity for cutting or for undesirable thermal damage tobiologic tissue while still permitting the thermal treatment level to bedelivered. To achieve the zig-zag pattern, the prisms in theabove-described geometry that have a rotation angle α applied to themcan also have an orthogonal tilt angle applied to produce the lateralspot displacements used to produce a zig-zag geometry.

In this example application, the family of output optical beams withdifferent deflection angles subsequently enters an imaging lens group19, as shown in FIGS. 2A and 2B, thus forming a pattern of spotsdisplaced along a line focus. Many imaging optics groups are possibleusing refractive, reflective, diffractive, or catadioptric forms. Thepreferred embodiment of FIGS. 2A-2B uses a solid catadioptric (“solidcat”) form which is easily manufactured and maintains freedom fromchromatic aberrations over a wide spectral range. FIG. 2A is a side viewof the optical pattern generator system (i.e., same view as FIG. 1A) andFIG. 2B is an end view of the system (i.e., viewer to the left in FIG.1A).

FIG. 2A shows a solid catadioptric imaging lens group 19 combined withthe rotating component 9 described above. In this view, only thereflective surfaces 21, 22 of the rotating component 9 are shown andthree different disk rotation positions are shown. The incident opticalbeam 20 is first reflected from surface 21 and then reflected fromsurface 22A. The optical beam enters the imaging lens group 19 and formsthe spot 27A. Two other positions of the rotating disk 9 are also shown.When the input optical beam 20 reflects from surface 21 and then fromsurface 22B, the spot 27B is formed. When the input optical beam 20reflects from surface 21 and then from surface 22C, the spot 27C isformed. Note that FIG. 2A shows an embodiment where the reflectingsurface 21 is at the same angle for all of the optical paths. This isnot a required condition and the geometry more frequently will usereflecting surfaces 21A, 21B and 21C with different angles and Cartesiancoordinates to achieve specific image array patterns.

FIGS. 2A-2B show the details of one embodiment of a solid cat imaginglens group. The optical beams exiting from the rotating component 19first enter a planar surface 28, are reflected from a planar minor 23,are reflected from a spherical minor 24, and exit from a planar surfacewhich in this case is a continuation of surface 23. Element 25 is anoptical window which seals the imaging lens group to maintain cleanoptical surfaces and item 26 is an optical window that for some biologicapplications is useful to maintain optical contact with the biologictissue being treated.

The geometry of this solid cat imaging lens group can be produced byclassical optical fabrication methods in a highly precise and costeffective manner. In one approach, the spherical reflecting surface 24is first produced in the material, and then the planar entry surface 28is generated into the spherical surface. The planar reflecting surface23 serves as the exit window. The geometry has an important advantageover other imaging lens groups in that the exit beams as shown in FIG.2A are essentially telecentric. Telecentric exit beam geometries areadvantageous for many biologic and industrial fabrication applications.

FIG. 3 shows a detailed view of the ray fans 30 that produce three imagespots 27 at the focal plane of the system. In FIG. 3, each of the threeimage points have three sets of ray fans that are associated with adifferent rotation angle of the corresponding sector as it rotatesthrough the incident optical beam. For example, ray fans 30A, 30B and30C are shown for image spot 27A. Ray fan 30A might correspond to thesector just entering the incident optical beam, fan 30B to a rotationangle midway through the optical beam and ray fan 30B to the sectorexiting the optical beam. Note that for the image spots 27, the opticalbeam moves slightly in the plane of the paper. For example, as shown inFIG. 3, ray fans 30A, 30B and 30C are slightly offset in angle withrespect to each other even though they converge at the same focus spot27A. Although three sets of ray fans are shown for clarity, there isactually a continuum of ray sets produced by the continuous movement ofthe respective sector through the incident optical beam.

For certain applications, the movement of the ray fans can haveadvantageous qualities. When the image spot is focused inside a tissuesuch as the human skin, the energy density is maximum for all rotationangles of the respective minor pair at the internal focal point, whilethe energy density pattern moves on the outer skin surface therebykeeping the thermal effects at the skin surface much lower than at theinternal treatment region. This condition can permit treatment ofinternal tissue features at high thermal levels while keeping theexternal tissue features at lower thermal levels and not producingunwanted damage to the tissue surface. The movement of the ray fansalong a target plane is also useful in applications such as seam weldingwhere long linear patterns can be used. It may be desired to operate thescanner with the target plane tilted and/or displaced relative to theimage plane in order to achieve the desired movement of the ray fans foreach of the beams.

FIG. 4 is a view of another optical pattern generator according to theinvention, where the direction of propagation for the incident opticalbeam 42 has a substantial component in a direction normal to the planeof rotation. This pattern generator also uses a single rotatingcomponent 40 with rotation axis 41 to generate the pattern of interest.In this example, the disk 40 supports reflective segments 43, 44 thatare rotated through the incident optical beam. The segments have parentoptical surfaces that are rotationally symmetric, with their opticalaxes coincident with the rotation axis 41 of the rotating component.FIG. 4 shows the large, parent optical surfaces with their smallerreflective segments 43, 44 where the beam 42 reflects twice and thenexits the pattern generator. In FIG. 4, the rotating component includesa disk 40 with pairs of opposing reflective surfaces 43, 44 for eachsector, where different sectors may contain reflective surfaces withdifferent radii of curvature such that the exiting beams will bedisplaced at different angles for each sector, but retain the PSDcondition. Because surfaces 43, 44 are rotationally symmetric and arerotated about their optical centerlines, both of the surfaces 43, 44that intersect with the optical beam are spatially invariant withrespect to rotation. The radii of the two reflective segments 43, 44 andtheir axial separation are chosen to keep the system approximatelyafocal for all segments while simultaneously varying the output beamangle.

FIG. 5A shows a side view of the optical pattern generator described inFIG. 4 combined with a reflective imaging lens group. Refractive anddiffractive imaging lens groups could also be used. The input beam 42 isreflected from the first surface segment 43 and then reflects from thesecond surface segment 44A. In this specific embodiment, the surfacesegment 43 is the same surface for all sequential segments whereas thesecond surface segment radius is different for each sequential segmentand is shown as 44A, 44B, and 44C. Variations of this embodiment arealso possible using different first surface radii for sequentialsegments and these segments would then be represented by 43A, 43B, and43C respectively. The variation in angular deflection from the rotatingcomponent would then be due to the different radii on the first surfacesegments 43.

For the specific embodiment where surface segment 43 remains the samefor all sequential optical paths, the surface segment may benon-rotating. For example, it may be firmly fixed to the imaging lensgroup 45 rather than to the disk 40.

In FIG. 5A, the imaging lens group 45 forms an image pattern comprisedof the three spots produced by three sequential sectors on the imageplane 53. For this optical pattern generator, the stigmatic (i.e.,sharply focused) images lie on a surface that is tilted with respect tothe optical axis of the imaging lens group 45. This image surface tiltis a consequence of the fact that only one of the surface segment pairscan have the two radii and separation distance that causes the exitingbeam to be collinear with the input beam and also have no refractivepower added to the beam. Other surface segment pairs require that theirradii and separation distance be chosen to achieve the desired outputbeam angular deviation. To make the angular deviation less than theoptical path that produces the collinear output beam, the firstreflective surface 43C generally becomes flatter or has an increasedradius of curvature while the second reflective surface 44C becomessteeper or has a decreased radius of curvature. This means that the twosurfaces no longer produce an afocal pair and positive power is added tothe output beam causing it to focus closer to the imaging lens group.When the output beam angular deflection is greater than the collinearoutput beam, the reverse occurs and negative power is added to theoutput beam so that it focuses further from the imaging lens group.

To achieve near diffraction-limited image spots, it is advantageous touse surface segments that are segments of aspheric surfaces ofrevolution with their optical axes coincident with the rotation axis 41of the system. Some applications can have larger image spots and forthese cases spherical surfaces of rotation can be acceptable.

For some applications that do not require high optical throughputefficiency, the beam is on for only a short portion of the rotationrange of each sector. The surface segments can be made toric aspheres sothe refractive power can be cancelled for each of the surface segmentpairs. This causes a small movement of the image spots as the surfacesegment pair rotates through the incident optical beam. The direction ofmovement is orthogonal to the direction that the spot is displaced fromthe system optical axis. The orthogonal image displacement is a functionof the toric power of the surfaces, so each spot in the image movesorthogonal to its displacement distance by a different amount. Thiscondition can be tolerated if the duty cycle (i.e. radiometricefficiency) of the system is low.

FIG. 5B shows a perspective view of FIG. 5A. The rotating disk 40 withits axis of rotation 41 is shown supporting two surface segments 43 and44, which are segments of aspheric surfaces of rotation with theircommon optical axes coincident with the rotation axis 41. As disk 40rotates, a different pair of surface segments (not shown) wouldintercept the incident optical beam 42 and change the deflection angleof the exiting optical beam 46 just before the optical beam enters theimaging lens group 45. The imaging lens group 45 comprises a firstplanar fold minor 50, an image forming minor 51 that is preferably ananamorphic aspheric surface to produce near diffraction-limited imagespots, and a second planar fold mirror 52 that directs the image to thepreferred location in space required for certain applications with longworking distances.

Applications that do not require near diffraction-limited image spotscan use image forming mirrors 51 that are toric in form such thatastigmatism is corrected or spherical in form if non-circular imagespots are acceptable for an application.

FIG. 5C is a top view of this embodiment that shows the folded geometryused in one embodiment of the imaging lens group. This folded geometryavoids self-obscuration of the optical path by using an off-axis segmentof an image forming minor 51 or a tilted segment of an image formingminor 51. This decentered geometry introduces astigmatism when the imageforming minor 51 is spherical in form. This astigmatism can be largelycorrected by making the image forming minor 51 toroidal or aspherictoroid in form. Further image correction is achieved by making the imageforming mirror 51 an anamorphic asphere which consists of two asphericshapes orthogonally oriented on the reflecting surface.

A variant of this embodiment is shown in FIG. 6 where the reflectingsurface segments 43, 44 are from parent surfaces which are toric oranamorphic aspheric in form. This variant provides both beam anglevariation for different optical paths and full correction of therefractive power so the rotating component is afocal and the imagesurface is normal to the system optical axis. Because the toric oranamorphic asphere segments 43, 44 change their profile as they arerotated, a small orthogonal displacement of the image spots which isdependent also upon spot linear displacement on the image surface willexist. For applications where the exposure period and therefore therotation angle is small, this variant configuration may be acceptable.

FIG. 7 is a view of another optical pattern generator using diffractiveelements to deflect an incident optical beam into a series of outputoptical beams. In FIG. 7, an input optical beam 70 is incident upon afold mirror 71 and then passes through a rotating disk 72 which has aseries of deflection sectors, each of which has diffractive opticalelement(s) located on the disk periphery. The disk 72 is rotated aboutits axis 73. Output optical beams 74 produced by different sectors areshown entering an imaging lens group 75, which forms a pattern on theimage surface 76. Each diffractive optical element has a differentspatial period such that each succeeding sector causes a differentangular deviation of the optical beam, which the imaging lens group 75focuses to a different spot along the focal line.

In a preferred embodiment, the diffractive elements uses diffractivestructures that are arctuate in form rather than parallel lines and thearctuate grooves have an axis that is coincident with the rotation axis73. This diffractive structure does not deflect the transmittedwavefront at a single angle but introduces a small angular variation ofthe wavefront which causes a small blurring of the image spots. Thisunwanted blurring can be partially corrected by the design of theimaging lens group so the image spots approach diffraction-limitedquality. The arctuate nature results in spatial invariance as eachsector rotates through the incident optical beam 70. A variant of thisembodiment uses reflective diffractive optical elements.

FIG. 8 is a view of another optical pattern generator according to theinvention. In this example, the rotating component has rotation axis 83.In FIG. 8, the input optical beam 80 first passes through the internalcylindrical surface 81 and subsequently through the cylindrical surface82. The cylindrical surfaces have a common rotation axis 83. Surface 82is divided into sectors, each containing optical elements. In FIG. 8,these optical elements are linear diffraction gratings with differentperiodicity. With respect to FIG. 8, the rulings of the grating run inthe direction perpendicular to the paper. Each diffractive gratingsurface deflects the output optical beam 84 by a different angle and theimaging lens group 85 forms a pattern of spots on the image surface 86.The use of linear gratings means that the sectors are spatiallyinvariant as they rotate through the optical beam 80.

In alternate embodiments, refractive or reflective optical elements mayalso be used. For example, reflective facets may act on the inputoptical beam at cylindrical surface 82, or refractive prisms may be usedon cylindrical surface 82. In addition, elements may be placed on bothsurfaces 81 and 82, for example to form a Z-shaped folded optical path,analogous to FIG. 4.

The above examples are discussed in the context of one incident opticalbeam and one output optical beam. The invention is not limited to thiscase. For example, referring to FIG. 1A, more than one optical beam maybe simultaneously incident on the sector shown. The optical beams may ormay not be overlapping. Overlapping beams may be combined upstream ofthe rotating component 9, for example by a wavelength-sensitive device,and then propagate together along the same optical path to the rotatingcomponent 9. Alternately, the optical beams may arrive at the same spotwithin a sector but from different angles. In FIG. 1A, a second sourcemight be located slightly above the plane of the paper but travel at aslight downward angle so that it is incident on the sector at the samelocation as optical beam 1 shown in FIG. 1A.

Alternately, the optical beams may not overlap at all. In FIG. 1A, theprisms may extend in the direction perpendicular to the paper and thesingle optical beam 1 may be replaced by an array of optical beams alsoextending in the direction perpendicular to the paper. As a finalexample, more than one sector may be active at a time. In FIG. 1A, theoptical beam 1 originates from the left and is incident at approximatelythe 7:30 position of rotating component 9. A second optical beam mayoriginate from the right and be incident at the symmetrical 4:30position. Optical beams can be incident at other positions also,although the subsequent imaging may become more complex.

The optical pattern generators described above can be used in manydifferent applications. Some examples of biological applications aredescribed in U.S. patent application Ser. No. 10/888,356 entitled“Method and Apparatus for Fractional Photo Therapy of Skin,” U.S. patentapplication Ser. No. 10/751,041 entitled “Multi-Spot Laser SurgicalApparatus and Method”, and U.S. Provisional Application No. 60/677,682entitled “Optically-Induced Treatment of Internal Tissue,” all of whichare incorporated herein by reference.

Various industrial applications will also be apparent. One example isshown in FIGS. 9A-9B. In this example, the optical pattern generatorshown in FIG. 1 is used to direct a laser beam 91 to various spots on aworkpiece 95 to produce weld joints 97. FIG. 9A shows a single laserbeam 91, deflected by one sector of the optical pattern generator 92 andfocused by lens 93 onto workpiece 95.

FIG. 9B shows a perspective view. In addition, two laser beams 91A-91Bare used simultaneously to produce two parallel rows of welds 97A-97B.FIG. 9B also shows the entire pattern of welds produced by all sectors.For each laser beam, each focus spot shown in FIG. 9B is produced by adifferent sector of the optical pattern generator 92.

FIG. 9C illustrates one row 97 of the welding pattern shown in FIG. 9B.There is a total of fifteen tack welds. The numbers show the order inwhich the welds are generated. Notice that the welds are not generatedin order from left to right. Instead, a far left weld 1 is generated andthen a far right weld 2 is generated. The remaining welds are selectedto tack long spans at their midpoints. For example, weld 3 tacksapproximately the middle of the span between welds 1 and 2; weld 4 tacksthe midpoint between 2 and 3 (which is the then-longest span); weld 5tacks approximately the middle between welds 1 and 3, etc.

This approach is advantageous because the initial two welds constrainthe part at both ends, thus reducing the need for clamping. In addition,the laser energy is distributed across the workpiece, thus avoidingexcess heat buildup as might be the case if the welds were madesequentially from left to right. Tacking the midpoints of long spansalso controls the effect of differential thermal expansion due to localheat buildup.

Due to symmetry in the welding pattern, the same effects may be realizedby starting with weld 9 rather than weld 1. This reduces the wait timebefore start of the welding pattern. If the workpiece is ready forwelding but the active sector is the one for weld 2, the device needonly wait until the sector for weld 9 rather than waiting for the entirepattern to cycle back to weld 1. Weld speeds of 1-10,000 welds persecond could be produced with the invention, preferably with weld speedsof hundreds or thousands of welds per second. As shown in FIG. 9D, thecontrol of thermal expansion can be optimized further if symmetry is notrequired for the scanner wheel. Other arrangements will be obvious tothose skilled in the art.

FIG. 10 illustrates another optical pattern generator according to theinvention. This optical pattern generator uses a single rotatingcomponent 1000 with rotation axis 1001 to generate the pattern ofinterest. In this example, each segment is comprised of a pair ofreflective surfaces 1003 and 1004, which are supported by the singlerotating component 1000. Three different rotational angles of the singlerotating component 1000 are superimposed in FIG. 1 to illustrate thedeflection of the incident optical beam 1002 from the pair of reflectivesurfaces 1003 and 1004 as the single rotating component is rotated. Thisrotation produces three separate positions for 1003 and 1004, which areillustrated as 1003A, 1003B, and 1003C; and 1004A, 1004B, and 1004Crespectively. The deflection angle of the incident optical beam ispreserved (because of the reflection off an even number of surfaces) asthe component 1000 is rotated.

Although the detailed description contains many specifics, these shouldnot be construed as limiting the scope of the invention but merely asillustrating different examples and aspects of the invention. It shouldbe appreciated that the scope of the invention includes otherembodiments not discussed in detail above. For example, the optical beamcan be incident at angles other than parallel to or normal to the planeof rotation of the rotating component. In addition, differentwavelengths can be used depending on the specific application.Generally, the term optical beam is used to refer to electromagneticradiation having at least half of its power in the wavelength range of200 to 12000 nm. Various other modifications, changes and variationswhich will be apparent to those skilled in the art may be made in thearrangement, operation and details of the method and apparatus of thepresent invention disclosed herein without departing from the spirit andscope of the invention as defined in the appended claims.

1. An optical pattern generator for generating a pattern of figures, theoptical pattern generator comprising: a rotatable component rotatingabout a rotation axis, the rotatable component comprising a plurality ofdeflection sectors arranged around the rotation axis, wherein each ofthe deflection sectors is configured to deflect a incident optical beamby a substantially constant angular deflection as each deflection sectorrotates through the incident optical beam, and each of the deflectionsectors deflects the incident optical beam by different angulardeflections to generate figures at different locations.
 2. The opticalpattern generator of claim 1 wherein the deflection sectors are arrangedapproximately in a circle that is centered on the rotation axis, thedeflection sectors are substantially self-compensating with respect to arotation of the rotatable component and are substantially spatiallyinvariant with respect to a wobble of the rotatable component, and theangular deflection is primarily in a plane of rotation of the rotatablecomponent.
 3. The optical pattern generator of claim 1 wherein thedeflection sectors are arranged approximately in a circle that iscentered on the rotation axis, and, for a majority of the deflectionsectors, the deflection sector comprises a pair of opposing reflectivesurfaces with surface normals that have a substantial component in aplane of rotation of the rotatable component.
 4. The optical patterngenerator of claim 3 wherein, for a majority of the deflection sectors,the incident optical beam is reflected from an even number of reflectivesurfaces in the deflection sector.
 5. The optical pattern generator ofclaim 3 wherein the rotatable component includes an odd number ofdeflection sectors.
 6. The optical pattern generator of claim 3 whereinthe reflective surfaces for at least some of the deflection sectorsintroduce an angular deflection with a component normal to the plane ofrotation, and the normal component of the angular deflection alternatesbetween two magnitudes as the deflection sectors rotate through theincident optical beam.
 7. The optical pattern generator of claim 1wherein the deflection sectors are arranged approximately in a circlethat is centered on the rotation axis, the deflection sectors aresubstantially self-compensating with respect to wobble of the rotatablecomponent and are substantially spatially invariant with respect torotation of the rotatable component, and the angular deflection isprimarily not in a plane of rotation of the rotatable component.
 8. Theoptical pattern generator of claim 1 wherein the deflection sectors arearranged approximately in a circle that is centered on the rotationaxis, and, for a majority of the deflection sectors, the deflectionsector comprises a pair of opposing reflective surfaces with surfacenormals that have a substantial component in a direction normal to theplane of rotation.
 9. The optical pattern generator of claim 1 furthercomprising: a first non-rotating reflective surface, wherein thedeflection sectors are arranged approximately in a circle that iscentered on the rotation axis, and, for a majority of the deflectionsectors, the deflection sector comprises a second reflective surfacewith a surface normal that does not have a substantial component in aplane of rotation of the rotatable component, the first and secondreflective surfaces forming a pair of opposing reflective surfaces fordeflecting the incident optical beam.
 10. The optical pattern generatorof claim 9 wherein each of the opposing reflective surfaces is a surfaceof revolution with optical axis coincident with the rotation axis. 11.The optical pattern generator of claim 1 further comprising: an imagingelement positioned to receive the deflected optical beams and to convertdifferent angular deflections into different beam positions on a targetsurface such that the figures move across the portion of the humantissue due to the rotation of the rotatable component.
 12. The opticalpattern generator of claim 1 further comprising: an imaging lens grouppositioned to receive the deflected optical beams and convert thedifferent constant angular deflections into different image positionswithin the pattern of figures, wherein each image position is stationaryas the corresponding deflection sector rotates through the incidentoptical beam.
 13. The optical pattern generator of claim 1 wherein thepattern of figures is an array of spots, and each of the spots issubstantially stationary as the corresponding deflection sector rotatesthrough the incident optical beam.
 14. The optical pattern generator ofclaim 13 wherein the spots are moved to compensate for relative motionof a workpiece.
 15. The optical pattern generator of claim 1 whereinparameters for the incident optical beam are selected to ablatematerial.
 16. The optical pattern generator of claim 1 whereinparameters for the incident optical beam are selected to cauterizematerial.
 17. The optical pattern generator of claim 1 whereinparameters for the incident optical beam are selected to treat humantissue.
 18. The optical pattern generator of claim 1 wherein therotatable component comprises a rotatable hollow cylindrical componentrotating about the rotation axis and including an arrangement ofdeflection sectors about the rotation axis, each deflection sectordeflecting the incident optical beam by a constant angular deflection asthe deflection sector rotates through the incident optical beam, and atleast two of the deflection sectors deflecting the incident optical beamby different angular deflections to generate figures at differentlocations.